1. Field of the Invention
This invention relates to improvements in control devices for fluid control systems and more particularly, but not by way of limitation, to a control and sequence valve assembly to permit automatic pressure activated start and stop operation of a positive displacement pumping system, or the like.
2. Description of the Prior Art
Many industrial and commercial pressure spray washing devices are in widespread use today, such as those utilized for cleaning parts and equipment, car washing establishments, and the like. These devices normally comprise a shutoff valve associated with a high pressure spray head, nozzle, or the like provided at one end of a high pressure fluid conduit. High pressure fluid is normally present at the shutoff valve at all times in order to provide pressure fluid for the cleaning operation. Any time the shutoff valve is abruptly closed, there is usually considerable pressure surge in the system which is frequently damaging to the shutoff valve and associate equipment. In addition, most of these devices or systems are of the fluid recirculating type using a basic unloading device to divert fluid flow back to the fluid reservoir of the apparatus, and the components of the apparatus are subjected to considerable wear during the recirculating period since the operating parts do not actually stop functioning. The devices presently available for use with high pressure spray apparatus or systems do not solve these problems. For example, U.S. Pat. No. 3,920,040 shows a device which is simply a pressure sensing pilot valve for closing and opening a main system shutoff valve in response to unusual fluid pressures in the system; U.S. Pat. No. 4,186,766 shows a device similar to that shown in the aforementioned patent in that it is simply a pressure sensing pilot valve for closing and opening a main system shutoff valve, which in this case is part of the device itself; U.S. Pat. No. 4,188,971 discloses a simple pressure or flow activated shutoff valve; and U.S. Pat. No. 4,063,489 relates to another version of "velocity fuse", or a flow activated shutoff valve. All of the devices of the aforementioned patents are based on the need to shutoff or shutdown some part of a fluid flow system and particularly a downstream portion of the system wherein the unusual pressure or flow condition may exist. All of these devices must be used in conjunction with appropriate controls to start or stop the pressure source and to prevent overpressuring of the pressure source. None of the devices will control the pressure source in any way, nor will they prevent overpressuring of the pressure source, or start or stop the pressure source on command. They will not automatically shut the pressure source down in a ninety percent unload condition, or start the pressure source in a totally unloaded condition.